Maarten ter Huurne wrote:
>
> At 09:24 AM 7/15/99 -0300, you wrote:
>
> >OPL1 is contained inside the OPL2 used by AdLib cards. The
> >OPL1 part of OPL2 chips is register-compatible with OPL1
> >chips and delivers exactly the same output.
>
> I thought that OPL2 didn't include the ADPCM part.
>
> Bye,
> Maarten
>
Hey ... Lemme talk about this ... I once used to fix some
Sound Blaster cards for friends ... (We can learn a lot of things about
hardware by just looking closely and thinking about. Also some
research on Internet helps a lot ! ) ;)
Sound blaster cards has a device called DSP , wich plays PCM data.
It relies on a DMA, some I/O ports and a IRQ channel.
It works as a sort of "buffered" PCM, It caches a "chunk" of the pcm
data sent by the PC microprocessor. When it finishes playing that
"chunk"
the DSP issues a IRQ signal , wich warns the PCM driver to transfer
another
data chunk to the DSP. That device is 100% independant from the fm synth
hardware.
Also , this DSP emulates the MIDI UART on the older SB 16 (non PNP)
cards.
On the MSXOPL (Y8950) by what I know the access to ADPCM device are
made within the
FM synth registers. (Correct me if I'm wrong , please)
The registers are organized somehow as this :
0xORG - 0xORG+3 OPL3 registers (In I/O order like 0x0C4 order for
OPL4 in MSX)
0xORG+4 - 0xORG+5 Mixer registers (ORG + 4 ADDR / ORG + 5 Data ,
Yamaha I/O Stile)
0xORG+6 DSP Reset
0xORG+8 - 0xORG+9 Mirror off 0xORG - 0xORG+1
0xORG+A DSP Read data
0xORG+C DSP Write data (Also DSP Status when read on.
Output in MSB)
0xORG+E DSP Status (MSB)
Fixed I/O (For ADLIB/ADLIB Gold compatibility)
0x388 - 0x38B Mirror of the OPL3 FM Synthetizer chip.
(The old Adlib & Adlib Gold cards had no PCM device)
All other ports inclued on the SB-PRO/16 hardware (Joystick & midi
port) were not
rellevant to be commented here ! ;)
The OPL3 chip used on PC sound cards could be really used easily to
partially emulate
MSX Audio (the ADPCM emulation , I think that could be a little tricky).
the hardware (the exeption is the FM part) is VERY diferent from the
MSX hardware.
I think people already didn't that because there is a HUGE distance
between speech and
a working thing . =) (Don't ya agree ?)
I hope I helped the understanding on that matter with this small info
...
Cya MSXers ...
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